1. The field of the Invention
The present invention relates to a method and apparatus for controlling a drive force of a vehicle, and in particular, to the method and apparatus for controlling a drive force in an vehicle's apparatus in which a running torque (i.e., the drive force) is transmitted from a drive source to a drive shaft via a torque transmission mechanism with a friction-jointed component.
2. Related Art
A conventional integration control system for a vehicle has been proposed, for example, by a United States Patent publication No. U.S. Pat. No. 6,292,741 B1. In this motor vehicle control system, a control system is divided into, at least, a body and compartment, vehicle movement, vehicle electric system, and driving apparatus, and then the driving apparatus is further divided into, at a minimum, a transmission, converter, and engine. Hence the entire control system is gradually divided into smaller systems, so that the entire control system is configured on a hierarchical structure. This hierarchical structure prevents not merely the vehicle control system from being complicated but also man hours necessary for developing the vehicle control system from being increased.
In cases where the entire vehicle system is hierarchised in its integration control, some of conventional different controls are treated at the same hierarchical level because those controls require the same actuator, even though the functional levels of those controls are different from each other. For instance, those controls include a cruise control, which has a function performed at a vehicle level and associates with plural types of controls, and an idling speed control, which has a function performed at an individual level and associates with only a closed control of the engine. Thus, since both the cruise control and the idling speed control are in common with each other in directly controlling an opening of a throttle valve, and those two types of controls are treated at the same level from a viewpoint of only an actuator, i.e., the throttle valve to be operated for achieving the controls. The processing required for the control has been made complicated.
To be specific, a confliction of the controls performed by the same actuator should be avoided. Because controlled variables and other variables for individual control functions are assigned to an actuator, it is necessary to have an additional control to decide which control has priority over the other controls or to give a compromise to those controls. If the actuator has no function for the priority or compromise control, there is a possibility that a conflict will occur among the controls and crews feel something is strange.
In contrast, in performing the vehicle integration control, each function for the integral control is processed as follows. A function at the vehicle level is subjected to control processing for managing the entire vehicle, resulting in that the function is translated into a function at an individual system level. The function at the individual system level is then subjected to control processing at an individual system, resulting in that the function is translated into a function at an actuator level. This results in that, for instance, the foregoing cruise control is executed as control processing at the vehicle level and the idling speed control is executed as control processing at the individual level. In those controls, the upper control processing is designed to perform the foregoing priority control or compromise (matching) control, so that the processing is avoided from being complicated and is executed based on an organized control structure.
The above integration control is not limited to the control of the throttle valve, but is applied to other various types of control, such as control of ignition timing at the engine and control of a regulator of the transmission.
However, when each set of control processing is properly arranged in the vehicle integration control, an inconvenience will occur as follows. It is sufficient for the conventional control that all the processing is carried out to calculate to an amount to be operated of an actuator for operating each function itself. However, it should be required that the integration control calculate, as amounts to be operated, physical amounts at the vehicle level, which are different from an amount to be operated by each actuator. In other words, in the integration control for providing functions at the vehicle level, the physical amounts to be operated should be calculated to be in common with various types of controls or to be applicable to various types of functions.
This calculation for the integration control will now be exemplified about the vehicle transmission, which includes an automatic transmission controlling a joint state of a clutch on controlled hydraulic pressure and a belt-type gearless transmission. In the case of the conventional control that is not carried out as the integration control, the processing carried for instructing the joint state of, for example, the clutch has figured out a hydraulic command value as the physical value for the control. On the other hand, the integration control is required to perform the processing for obtaining a proper operated amount that realizes a function at the vehicle level. Thus, in the case of the processing for commanding the joint state of the clutch, it is required that the processing be carried out to have a physical variable nearer to the vehicle level than a hydraulic command value.
For instance, as shown in Japanese Patent Laid-open publication No. 5-209678, there has been known an apparatus for controlling an output of a drive unit. In this apparatus, employed is a torque-base control that uses engine torque for a physical variable in the control processing.
In the conventional or torque-base control, a premise is made such that, when the engine is controlled to have a desired torque value at a transmission output shaft or drive shaft, a joint state of a friction joint component intervening between the engine and the transmission will not fluctuate whenever any amount of torque is inputted from the engine or transmission. In other words, the conventional technique takes it into account a slip ratio (i.e., transmitted ratio) at a torque converter through which a running torque is transmitted from the engine to the torque converter and transmission.
However, actually, the joint state of the friction joint component varies depending on the magnitude of torque inputted from the engine and torque converter. By way of example, when it is supposed that the transmission according to the conventional technique is provided with a planetary gear and a clutch, there is a premise that the clutch in the transmission provides a complete connected state or a complete disconnected state in any case when the torque is transmitted from the engine and torque converter to the transmission.
However, the joint state of the clutch changes any time depending on gear changes and others. Thus, compared to the torque converter controlled to transmit a necessary amount of torque, the clutch is subjected to a larger number of uncertain factors. When a transmission-output-shaft torque or wheel-rotation torque is adjusted to a desired amount, it is therefore necessary to pay attention to the transmission torque at the friction joint component that varies depending on various factors. With no such a consideration taken, it is impossible to realize the engine output control preventing an improper slip at the friction joint component.